U.S. patent number 6,982,544 [Application Number 10/942,546] was granted by the patent office on 2006-01-03 for system and method of battery capacity reporting.
This patent grant is currently assigned to Research In Motion Limited. Invention is credited to Phat H. Tran.
United States Patent |
6,982,544 |
Tran |
January 3, 2006 |
System and method of battery capacity reporting
Abstract
A method and system for accurately reporting battery capacity is
disclosed herein. The disclosed method and system prevent the
reporting of discontinuous capacity values resulting from starting
or stopping recharge cycles. The disclosed method and system
prevent over or under reporting of battery capacity due to the
transition between charge and discharge curves in a battery
model.
Inventors: |
Tran; Phat H. (Kitchener,
CA) |
Assignee: |
Research In Motion Limited
(Waterloo, CA)
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Family
ID: |
23170663 |
Appl.
No.: |
10/942,546 |
Filed: |
September 16, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050029988 A1 |
Feb 10, 2005 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10189714 |
Jul 3, 2002 |
6794852 |
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60303129 |
Jul 5, 2001 |
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Current U.S.
Class: |
320/132 |
Current CPC
Class: |
H02J
7/0047 (20130101); G01R 31/3828 (20190101); H01M
10/48 (20130101); G01R 31/3648 (20130101); H02J
7/0048 (20200101); Y02E 60/10 (20130101) |
Current International
Class: |
H01M
10/46 (20060101) |
Field of
Search: |
;320/132,134,135,136,DIG.21,149 ;324/427,432,433 ;429/90,100
;D13/103 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Smart Battery System (SMBus) @ http://www.smbus.org/, Intel Corp.,
Feb. 15, 1995 (1 pg). cited by other.
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Primary Examiner: Tso; Edward H.
Attorney, Agent or Firm: Day; Jones Pathiyal; Krishna K.
Liang; Robert C.
Parent Case Text
This is a continuation of Ser. No. 10/189,714, filed Jul. 3, 2002
now U.S. Pat. No. 6,794,852 which claims the benefit of Provisional
Application No. 60/303,129, filed Jul. 5, 2001.
Claims
What is claimed is:
1. A method for reporting an available capacity of a rechargeable
battery, comprising: reporting the available capacity of the
rechargeable battery based on a measured battery voltage; detecting
a change in state of the rechargeable battery between a discharge
state and a charge state; if the detected state change is from the
charge state to the discharge state, then reporting only decreases
in the available capacity until another state change is detected;
and if the detected state change is from the discharge state to the
charge state, then reporting only increases in the available
capacity until another state change is detected.
2. The method of claim 1, wherein the available capacity is
determine from the measured battery voltage using a capacity
model.
3. The method of claim 2, wherein: if the rechargeable battery is
in the discharge state, then the available capacity is determined
using a discharge curve from the capacity model; and if the
rechargeable battery is in the charge state, then the available
capacity is determined using a charge curve from the capacity
model.
4. The method of claim 1, further comprising: if the detected state
change is from the charge state to the discharge state and a
determined value of the available capacity has increased from a
last reported capacity, then continuing to report the last reported
capacity; and if the detected state change is from the discharge
state to the charge state and the determined value of the available
capacity has decreased from the last reported capacity, then
continuing to report the last reported capacity.
5. The method of claim 1, wherein the determination as to whether
the available capacity is increasing or decreasing is made by
comparing a candidate capacity with a last reported capacity.
6. The method of claim 1, wherein the measured battery voltage is
corrected based on a measured battery current and an effective
serial resistance, and wherein the reported available capacity is
determined based on the corrected measured battery voltage.
7. The method of claim 6, wherein the measured battery voltage is
further corrected to compensate for temperature fluctuations.
8. A method for reporting an available capacity of a rechargeable
battery, comprising: reporting the available capacity of the
rechargeable battery based on a measured battery voltage; detecting
a change in state of the rechargeable battery between a discharge
state and a charge state; if the detected state change is from the
charge state to the discharge state, then using a fast convergence
rate to report the battery available capacity if the measured
battery voltage is decreasing and using a slow convergence rate to
report the available battery capacity if the measured battery
voltage is increasing; and if the detected state change is from the
discharge state to the charge state, then using the fast
convergence rate to report the available battery capacity if the
measured battery voltage is increasing and using the slow
convergence rate to report the available battery capacity if the
measured battery voltage is decreasing.
9. The method of claim 8, further comprising: if the slow
convergence rate is to be used to report the available battery
capacity, then first determining if a target battery capacity to be
reported using the slow convergence rate is within a play range of
a last reported capacity, and if the target battery capacity is not
within the play range, then continuing to report the last reported
capacity.
10. The method of claim 8, wherein the available capacity is
determine from the measured battery voltage using a capacity
model.
11. The method of claim 10, wherein: if the rechargeable battery is
in the discharge state, then the available capacity is determined
using a discharge curve from the capacity model; and if the
rechargeable battery is in the charge state, then the available
capacity is determined using a charge curve from the capacity
model.
12. The method of claim 9, wherein the play range is determined as
a function of the state of the rechargeable battery and the last
reported capacity.
13. The method of claim 8, wherein the measured battery voltage is
corrected based on a measured battery current and an effective
serial resistance, and wherein the reported available capacity is
determined based on the corrected measured battery voltage.
14. The method of claim 13, wherein the measured battery voltage is
further corrected to compensate for temperature fluctuations.
15. A handheld device having a system for reporting an available
capacity of a rechargeable battery, comprising: a charging
subsystem configured to determining the available capacity of the
rechargeable battery based on a measured battery voltage; a user
interface configured to report the available capacity; the charging
subsystem being further configured to detect a change in state of
the rechargeable battery between a discharge state and a charge
state; wherein if the detected state change is from the charge
state to the discharge state, then the charging subsystem being
configured to report only decreases in the available capacity until
another state change is detected; and wherein if the detected state
change is from the discharge state to the charge state, then the
charging subsystem being configured to report only increases in the
available capacity until another state change is detected.
16. The handheld device of claim 15, wherein if the detected state
change is from the charge state to the discharge state and a
determined value of the available capacity has increased from a
last reported capacity, then the charging subsystem being
configured to continue reporting the last reported capacity; and if
the detected state change is from the discharge state to the charge
state and the determined value of the available capacity has
decreased from the last reported capacity, then the charging
subsystem being configured to continue reporting the last reported
capacity.
17. The handheld device of claim 15, wherein the charging subsystem
determines whether the available capacity is increasing or
decreasing by comparing a candidate capacity with a last reported
capacity.
18. A handheld device having a system for reporting an available
capacity of a rechargeable battery, comprising: a charging
subsystem configured to determining the available capacity of the
rechargeable battery based on a measured battery voltage; a user
interface configured to report the available capacity; the charging
subsystem being further configured to detect a change in state of
the rechargeable battery between a discharge state and a charge
state; wherein if the detected state change is from the charge
state to the discharge state, then the charging subsystem being
configured to use a fast convergence rate to report the battery
available capacity if the measured battery voltage is decreasing
and to use a slow convergence rate to report the available battery
capacity if the measured battery voltage is increasing; and wherein
if the detected state change is from the discharge state to the
charge state, then the charging subsystem being configured to use
the fast convergence rate to report the available battery capacity
if the measured battery voltage is increasing and to use the slow
convergence rate to report the available battery capacity if the
measured battery voltage is decreasing.
19. The handheld device of claim 18, wherein if the slow
convergence rate is to be used to report the available battery
capacity, then the charging subsystem being configured to determine
if a target battery capacity to be reported using the slow
convergence rate is within a play range of a last reported
capacity, and if the target battery capacity is not within the play
range, then continuing to report the last reported capacity.
20. The handheld device of claim 19, wherein the play range is
determined as a function of the state of the rechargeable battery
and the last reported capacity.
Description
FIELD OF THE INVENTION
The present invention relates generally to batteries. More
particularly, the present invention relates to reporting of the
capacity of a battery.
BACKGROUND OF THE INVENTION
Many mobile computing and communicating devices rely upon standard
battery cells for providing power on which to operate. Though
disposable battery cells, such as alkaline cells, are a well-known
and reliable technology, it is common in such mobile devices to
employ rechargeable battery cells. These rechargeable batteries
depend on a number of known cell types, including Ni-Cad, Ni-MH,
and Li-Ion cells. All these cells are known to those of skill in
the art, as are some of their deficiencies. One of the known
deficiencies of the above mentioned rechargeable battery cells is
related to the fact that each battery has a finite life span that
can be measured in terms of recharge cycles. The process of
charging and discharging the cell damages the cell's charge storage
capabilities, causing the stored potential, which is typically
measured in mA-hours, to decrease over the life of the battery. As
the ability to store charge decreases, so does the battery's
utility. The life of the battery can be drastically curtailed by
improperly charging, or over discharging the battery. Another known
deficiency of the above cell types is that the batteries are known
to discharge while in storage, though some types of battery are
more susceptible to the self-discharge phenomenon than others. As a
result of these deficiencies, it is crucial that a user be able to
determine the capacity of a battery both prior to and during
use.
A state of the art technique for battery capacity reporting relies
on the coulomb counter. The principle of operation involved in
coulomb counting is computing a coulomb count equal to the coulombs
injected into a battery minus the coulombs taken out of the
battery. The capacity of the battery is then reported by comparing
the coulomb count relative to a reference coulomb count value that
corresponds to maximum battery capacity. For instance, if the
coulomb count of a battery is half of the reference value, the
battery capacity is reported to be 50 percent. Although the coulomb
counter addresses battery capacity reporting, it may have several
problems. First, the reported capacity may not be meaningful if an
accurate reference coulomb count value corresponding to maximum
battery capacity is not known. Furthermore, with a coulomb counter
it may be difficult to keep an accurate reference coulomb count,
particularly when battery capacity decreases over the lifetime of
the battery. Further still, with a coulomb counter it may be
necessary to know the current battery capacity before beginning the
coulomb count.
A limitation of the coulomb counting principle is that it may not
be applicable to reporting the capacity of a battery of initially
unknown battery capacity: if the capacity of a battery is to be
reported using the coulomb count system and method, the battery may
have to be taken from it's unknown capacity state to either a fully
charged 100 percent battery capacity state or to a fully discharged
0 percent capacity state before the coulomb count can be used.
Because the state of the battery is unknown at a certain point, the
only way to charge the battery to 100% capacity is to constantly
provide charge over an extended length of time. This can result in
an overcharging of the cell, which is known to damage to the
storage capability of the cell. Conversely, to guarantee that the
cell is at 0% capacity, the cell must be completely discharged. It
is a known phenomenon that rechargeable batteries are damaged by a
full discharge to a complete empty state. Thus forcing a battery to
either 100% or 0% capacity will likely damage the cell, which only
hastens the time at which the coulomb counting becomes
inaccurate.
Further practical limitations exist with coulomb counting
techniques. In practice, coulomb counting works by applying an
integration over time. The presence of an offset in a coulomb
counter may result in the inaccuracy of the coulomb count. This
applies even to batteries with an assumed initially known battery
capacity, and is compounded with every recharge cycle. This may be
especially true if the battery needs to be used for a long period
of time between opportunities to reset the coulomb counter. For
instance, in a battery that needs to be used for 3 weeks between
charges, even small offsets with each charge cycle may accumulate
to large inaccuracies in reported capacity.
Other known techniques of battery capacity reporting exist, and are
primarily based on measuring battery voltage. The interest in such
voltage techniques is due to the technical ease involved in voltage
measurement. However, voltage measurement techniques also present
the greatest challenges since the relationship between battery
voltage and battery capacity is plastic, i.e. for any given battery
capacity, the measured battery voltage can vary greatly. The
presence of such variations prevent the systematic reporting of
meaningful battery capacity values. The variations are small if the
current draw is fairly constant over the lifetime of the battery,
so there are situations where a direct voltage to capacity mapping
will suffice.
Many battery capacity reporting solutions assume a fairly constant
current draw for the major mode of operation, and only report
capacity in this mode. For example, most cell phones only report
battery capacity when they are not charging. Once they start
charging, their battery gauges stop indicating battery capacity.
However, in applications where a battery is recharged while the
system is running, such a change in state from discharging to
charging, or vice versa, may break any assumptions about constant
current draw.
Batteries have known characteristic charge and discharge curves.
FIG. 1 illustrates a charge curve 140 and a discharge 130 curve for
a battery. These curves relate battery voltage 120 to percent
capacity 110 for a rechargeable battery. The curves provide a model
100 for a battery. In the model, percent battery capacity 110 is
related to battery voltage 120 in either a discharging state, shown
by discharge curve 130, or the charging state shown by charge curve
140. Illustrated is a multiplicity of points such as point 132 on
the discharging curve 130 and of point 142 on the charging curve.
Interpolation can be used to provide capacity values 110 for
voltages 120 that lie between points for which values are
known.
In reference to FIG. 1, the details of a charge state capacity
model 100 are described. The relationship between battery voltage
110, battery charge state and capacity 120 is illustrated by two
curves 130,140. A first curve 140 corresponds to a positive battery
charge current or charging battery charge state, and a second curve
130 corresponds to a negative battery charge current or discharging
battery charge state.
Although not expressly shown in the drawings, the charge state
capacity model 100 can use more than one pair of curves. Each curve
is a function of both the battery charge current and the battery
charge state. The charge state is used to select at least one curve
from a multiplicity of charge curves. Each curve is a function of
the battery charging current, and relates battery voltage to
capacity. For example, when the battery is in a first charge state,
such as the charging state, a first charge curve corresponding to
the charging state is utilised. When the battery is in a second
charge state, for instance the discharging state, a second charge
curve corresponding to the discharge state is utilised. The charge
curves are such that given a battery voltage value and a charge
curve, it is possible to obtain a corresponding capacity value from
the charge curve.
Though it is possible to determine the capacity of a battery by
measuring the voltage of the battery and examining the model, it
should be noted that the existence of two distinct curves presents
a problem. When a battery is charging and is at 50% capacity, it
has a defined voltage level. If the battery charging is terminated
when the battery is at 50%, the voltage of the battery does not
instantly decrease to the voltage that corresponds to 50% capacity
on the discharge curve. Instead the voltage decays to that level
over time. The voltage of a 50% battery in a charging state is
equivalent to the voltage of a 60 70% battery in the discharging
state. As a result, most voltage based battery capacity reporting
devices report a capacity jump when charging is ended. Similarly,
there is a reported battery capacity drop when charging is started.
These abrupt changes in capacity are inaccurate, and cause
confusion among users.
There remains a further need for a system and method of battery
capacity reporting based on battery voltage that overcomes the
limitations present in the plastic relationship between battery
voltage and battery capacity.
There remains a further need still for a system and method of
battery capacity reporting which systematically reports a
meaningful battery capacity value whether the battery is being
discharged or charged, and which does so regardless of the presence
of transitions between the charging and discharging of the
battery.
SUMMARY OF THE INVENTION
It is an object of the present invention to obviate or mitigate at
least one disadvantage of previous battery capacity reporters. It
is a further object of the present invention to provide a system
and method for battery capacity reporting based on battery voltage
that is robust against inaccuracies in initial battery capacity
estimations and which systematically provides a meaningful reported
battery capacity value.
In a first aspect, the present invention provides a method of
determining the available battery capacity of a battery. In the
method, a battery voltage and a current charge state of the battery
are determined. These determined values are then used to determine
a target battery capacity. The determined battery capacity is
compared to a previous battery capacity, and the target battery
capacity is adjusted if the comparison is not indicative of the
determined charge state. In an embodiment of the present invention,
the method further includes either or both of the steps of
reporting the target battery capacity and storing the reported
capacity as the previous battery capacity.
In a further embodiment of the first aspect of the present
invention the two defined charge states are a charging state, and a
discharging state. In the charging state, a target battery capacity
less than the previous battery capacity is not indicative of the
charge state, while a target battery capacity greater than the
previous battery capacity is not indicative of the discharging
state. In a further embodiment, determining the battery capacity is
done by examining a predetermined model of the correlation between
voltage, charge state and capacity.
In other embodiments of the present invention adjusting the target
capacity can involve changing the target capacity to the value of
the previous battery capacity value or changing the target capacity
to a capacity determined from a predefined fast transition curve
that models the relationship between the determined battery
voltage, the determined current charge state and battery capacity.
In a further embodiment to the first aspect of the present
invention, there is provided , prior to the step of reporting, an
adjustment step for adjusting the target capacity to a capacity
determined from a predefined slow transition curve. The slow
transition curve models the relationship between the determined
battery voltage, the determined current charge state and battery
capacity, when the target capacity is in a play region around the
capacity of the battery when the last change in charge state
occurred.
Further aspects of the first aspect of the present invention
provide a further adjustment of the target battery capacity based
on an effective serial resistance correction factor or to
compensate for temperature fluctuations.
A second aspect of the present invention provides a system for
determining the capacity of a battery with a memory for storing a
previous battery capacity value. The system has voltage reading
means, charge state determining means, target capacity determining
means, a comparator and target capacity adjusting means. The
voltage reading means are operatively connected to the battery to
determine the voltage of the battery. The charge state determining
means are operatively connected to the battery to determine the
charge state of the battery. The target capacity determining means,
are operatively connected to the voltage reading means to receive
the determined voltage and to the charge state determining means to
receive the determined charge state, so that they can compute a
target battery capacity based on the determined voltage and the
determined charge state. The comparator is operatively connected to
the memory to receive the previous battery capacity value and to
the target capacity determining means to receive the target battery
capacity, it generates a comparison signal representative of the
comparison of the previous battery capacity value and the target
battery capacity. The target capacity adjusting means are
operatively connected to the comparator to receive the comparison
signal, to the target capacity determining means to receive the
determined target battery capacity and to the charge state
determining means to receive the determined charge state. The
target capacity adjusting means adjust the determined target
battery capacity if the comparison signal is not indicative of the
determined charge state, and they also store the adjusted target
battery capacity in the memory.
In an embodiment of the second aspect of the present invention
there is provided reporting means, operatively connected-to the
target capacity adjusting means for reporting the adjusted target
battery capacity.
In various embodiments, the target capacity adjusting means further
includes means for a number of functions. One such function is to
adjust the determined target capacity to a capacity determined from
a predefined fast transition curve that models the relationship
between the determined battery voltage, the determined current
charge state and battery capacity after a change in charge state.
Another such function is to adjust the target capacity to a
capacity determined from a predefined slow transition curve that
models the relationship between the determined battery voltage, the
determined current charge state and battery capacity when the
target capacity is in a play region around the capacity of the
battery when the last change in charge state occurred.
In another embodiment the target capacity adjusting means is also
connected to an effective serial resistance tester which is
operatively connected to the battery to determine an effective
serial resistance correction factor, the target capacity adjusting
means further includes means for adjusting the target capacity
based on the effective serial resistance correction factor.
In a presently preferred aspect the above described system is
integrated into a handheld computing or communicating device.
Other aspects and features of the present invention will become
apparent to those ordinarily skilled in the art upon review of the
following description of specific embodiments of the invention in
conjunction with the accompanying FIGS.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described, by way
of example only, with reference to the attached FIGS., wherein:
FIG. 1 illustrates two curves, a charge and a discharge curve,
relating battery voltage to percent capacity for a rechargeable
battery, in accordance with the present invention;
FIG. 2 is a block diagram of a mobile communication device in which
the instant invention may be implemented;
FIG. 3 is a flowchart illustrating a preferred embodiment of the
method of battery capacity reporting, in accordance with the
present invention;
FIG. 4 is an enlarged version of a portion of FIG. 1, the portion
bound by a dotted rectangle in FIG. 1;
FIG. 5 illustrates a transition from the use of the charge curve to
the use of the discharge curve of FIG. 4 in a first embodiment of a
method to carry out step 260 of FIG. 3, in accordance to the
present invention;
FIG. 6 illustrates a transition from the use of the discharge curve
to the use of the charge curve of FIG. 4 in a first embodiment of a
method to carry out step 260 of FIG. 3, in accordance to the
present invention;
FIG. 7 is a flowchart illustrating a first embodiment of a method
to carry out step 260 of FIG. 3, in accordance with FIGS. 5 and
6;
FIG. 8 illustrates a transition from the last reported capacity
towards the discharge curve of FIG. 4 in a preferred embodiment of
a method to carry out step 260 of FIG. 3, in accordance to the
present invention;
FIG. 9 illustrates a transition from the last reported capacity
towards the charge curve of FIG. 4 in a preferred embodiment of a
method to carry out step 260 of FIG. 3, in accordance with the
present invention;
FIG. 10 is a flowchart illustrating a preferred embodiment of a
method to carry out step 260 of FIG. 3, in accordance with FIGS. 8
and 9; and
FIG. 11 is a block diagram illustrating an exemplary embodiment of
a system of the present invention.
DETAILED DESCRIPTION
Generally, the present invention provides a method and system for
measuring and reporting battery capacity.
FIG. 2 is a block diagram of a mobile communication device 10 in
which the instant invention may be implemented. The mobile
communication device 10 is preferably a two-way communication
device having at least voice or data communication capabilities.
The device preferably has the capability to communicate with other
computer systems on the Internet. Depending on the functionality
provided by the device, the device may be referred to as a data
messaging device, a two-way pager, a cellular telephone with data
messaging capabilities, a wireless Internet appliance or a data
communication device (with or without telephony capabilities). It
will be apparent to one of skill in the art that batter capacity
reporting and measurement has applications that are not limited to
the field of mobile communicating and computing devices.
Where the device 10 is enabled for two-way communications, the
device will incorporate a communication subsystem 11, including a
receiver 12, a transmitter 14, and associated components such as
one or more, preferably embedded or internal, antenna elements 16
and 18, local oscillators (LOs) 13, and a processing module such as
a digital signal processor (DSP) 20. As will be apparent to those
skilled in the field of communications, the particular design of
the communication subsystem 11 will be dependent upon the
communication network in which the device is intended to operate.
For example, a device 10 destined for a North American market may
include a communication subsystem 11 designed to operate within the
Mobitex.TM. mobile communication system or DataTAC.TM. mobile
communication system, whereas a device 10 intended for use in
Europe may incorporate a General Packet Radio Service (GPRS)
communication subsystem 11.
Network access requirements will also vary depending upon the type
of network 19. For example, in the Mobitex.TM. and DataTAC.TM.
networks, mobile devices such as 10 are registered on the network
using a unique personal identification number or PIN associated
with each device. In GPRS networks however, network access is
associated with a subscriber or user of a device 10. A GPRS device
therefore requires a subscriber identity module (not shown),
commonly referred to as a SIM card, in order to operate on a GPRS
network. Without a SIM, a GPRS device will not be fully functional.
Local or non-network communication functions (if any) may be
operable, but the device 10 will be unable to carry out any
functions involving communications over network 19. When required
network registration or activation procedures have been completed,
a device 10 may send and receive communication signals over the
network 19. Signals received by the antenna 16 through a
communication network 19 are input to the receiver 12, which may
perform such common receiver functions as signal amplification,
frequency down conversion, filtering, channel selection and
analog-digital conversion. Analog to digital conversion of a
received signal allows complex communication functions, such as
demodulation and decoding, to be performed in the DSP 20. In a
similar manner, signals to be transmitted are processed, including
modulation and encoding for example, by the DSP 20 and input to the
transmitter 14 for digital to analog conversion, frequency up
conversion, filtering, amplification and transmission over the
communication network 19 via the antenna 18.
The DSP 20 not only processes communication signals, but also
provides for receiver and transmitter control. For example, the
gains applied to communication signals in the receiver 12 and
transmitter 14 may be adaptively controlled through automatic gain
control algorithms implemented in the DSP 20.
The device 10 preferably includes a microprocessor 38 which
controls the overall operation of the device. Communication
functions, including at least one of data and voice communications,
are performed through the communication subsystem 11. The
microprocessor 38 also interacts with further device subsystems
such as the display 22, flash memory 24, random access memory (RAM)
26, auxiliary input/output (I/O) subsystems 28, serial port 30,
keyboard 32, speaker 34, microphone 36, a short-range
communications subsystem 40 and any other device subsystems
generally designated as 42.
Some of the subsystems shown in FIG. 2 perform
communication-related functions, whereas other subsystems may
provide "resident" or on-device functions. Notably, some
subsystems, such as keyboard 32 and display 22 for example, may be
used for both communication-related functions, such as entering a
text message for transmission over a communication network, and
device-resident functions such as a calculator or task list.
Operating system software used by the microprocessor 38 is
preferably stored in a persistent store such as flash memory 24,
which may instead be a read only memory (ROM) or similar storage
element (not shown). Those skilled in the art will appreciate that
the operating system, specific device applications, or parts
thereof, may be temporarily loaded into a volatile store such as
RAM 26. It is contemplated that received communication signals may
also be stored to RAM 26.
The microprocessor 38, in addition to its operating system
functions, preferably enables execution of software applications on
the device. A predetermined set of applications which control basic
device operations, including at least data and voice communication
applications for example, will normally be installed on the device
10 during manufacture. A preferred application that may be loaded
onto the device may be a personal information manager (PIM)
application having the ability to organise and manage data items
relating to the device user such as, but not limited to e-mail,
calendar events, voice mails, appointments, and task items.
Naturally, one or more memory stores would be available on the
device to facilitate storage of PIM data items on the device. Such
PIM application would preferably have the ability to send and
receive data items, via the wireless network. In a preferred
embodiment, the PIM data items are seamlessly integrated,
synchronised and updated, via the wireless network, with the device
user's corresponding data items stored or associated with a host
computer system thereby creating a mirrored host computer on the
mobile device with respect to the data items at least. This would
be especially advantageous in the case where the host computer
system is the mobile device user's office computer system. Further
applications may also be loaded onto the device 10 through the
network 19, an auxiliary I/O subsystem 28, serial port 30,
short-range communications subsystem 40 or any other suitable
subsystem 42, and installed by a user in the RAM 26 or preferably a
non-volatile store (not shown) for execution by the microprocessor
38. Such flexibility in application installation increases the
functionality of the device and may provide enhanced on-device
functions, communication-related functions, or both. For example,
secure communication applications may enable electronic commerce
functions and other such financial transactions to be performed
using the device 10.
In a data communication mode, a received signal such as a text
message or web page download will be processed by the communication
subsystem 11 and input to the microprocessor 38, which will
preferably further process the received signal for output to the
display 22, or alternatively to an auxiliary I/O device 28. A user
of device 10 may also compose data items such as email messages for
example, using the keyboard 32, which is preferably a complete
alphanumeric keyboard or telephone-type keypad, in conjunction with
the display 22 and possibly an auxiliary I/O device 28. Such
composed items may then be transmitted over a communication network
through the communication subsystem 11.
For voice communications, overall operation of the device 10 is
substantially similar, except that received signals would
preferably be output to a speaker 34 and signals for transmission
would be generated based on an input received through a microphone
36. Alternative voice or audio I/O subsystems such as a voice
message recording subsystem may also be implemented on the device
10. Although voice or audio signal output is preferably
accomplished primarily through the speaker 34, the display 22 may
also be used to provide an indication of the identity of a calling
party, the duration of a voice call, or other voice call related
information for example.
The serial port 30 in FIG. 2 would normally be implemented in a
personal digital assistant (PDA)-type communication device for
which synchronisation with a user's desktop computer (not shown)
may be desirable, but is an optional device component. Such a port
30 would enable a user to set preferences through an external
device or software application and would extend the capabilities of
the device by providing for information or software downloads to
the device 10 other than through a wireless communication network.
The alternate download path may for example be used to load an
encryption key onto the device through a direct and thus reliable
and trusted connection to thereby enable secure device
communication.
A short-range communications subsystem 40 is a further optional
component which may provide for communication between the device 10
and different systems or devices, which need not necessarily be
similar devices. For example, the subsystem 40 may include an
infrared device and associated circuits and components or a
Bluetooth.TM. communication module to provide for communication
with similarly-enabled systems and devices.
A charging subsystem 44 is a component that provides power for the
device 10 and different subsystems or devices. For example, the
charging subsystem 44 may determine the presence of detachable
power source device 46 and associated circuits, such as an AC
adapter, USB bus, or car adapter to provide power for the device
and to charge battery 48. Additionally, charging subsystem 44 may
determine the absence of power source device 46, and consequently
obtain power for the device 10 from battery 48. When the battery 48
powers device 10, the battery 48 is said to be in a discharging
state. Conversely, when power source device 46 powers device 10,
and charging subsystem charges battery 48, the battery is said to
be in a charging state. The present invention is concerned with
reporting the capacity of a battery such as battery 48.
The battery capacity reported is a function of several factors,
including battery voltage, and battery charging current. The
relationship between battery voltages, battery charging currents,
and battery capacity is modelled using charge curves such as those
illustrated in FIG. 1. Therefore, before describing embodiments of
the method and system in detail, several concepts will be defined
for greater certainty.
As used in this description and in the appended claims, the battery
voltage is defined as the voltage differential between positive and
negative terminals of the battery.
As used in this description and in the appended claims, the battery
charging current is defined as a current flow into the battery.
Battery charging current is capable of taking on a signed value,
with a positive value meaning current being delivered into the
battery and a negative value meaning current drawn out of the
battery.
As used in this description and in the appended claims, charge
state, also referred to as charging state, is defined as the sign
of the corresponding battery charging current. Therefore reference
to a positive charge state is synonymous with charging. Similarly,
a negative charge state is synonymous with discharging. The use of
either term is clear and unambiguous.
As used in this description and in the appended claims, a capacity
model is defined as the relationship between battery voltage,
battery charging current, and capacity so that given battery
voltage and battery charging current, capacity can be determined by
applying the capacity model.
Generally, the method of the present invention adjusts the reported
battery capacity to eliminate abrupt discontinuities in the
reported battery capacity. The charging state of the battery is
determined, and is used to select either the charge or the
discharge curve. The voltage of the battery is then read, and using
the selected curve a preliminary, or target, capacity is
determined. The preliminary capacity is compared to the last
reported capacity. The comparison will show an increase in battery
capacity while the battery is in a discharge state if the charging
has been discontinued, or conversely will show a decrease in
capacity while the battery is in the charge state if the charging
has been started. Because this is known to be inaccurate, an
adjustment is made in the preliminary battery capacity, and the
adjusted capacity is reported. The reported capacity is then stored
for use in the next cycle. The method of adjustment of the battery
capacity can be as simple as reporting the previously reported
value until the battery capacity follows the known charge and
discharge curves, or it can involve an analysis of the reported
voltage and a comparison of the reported voltage to a previously
reported voltage to create a new curve through which the battery
capacity varies. The methods of the adjustment are described in
greater detail below.
Referring to FIGS. 1 and 2, in a preferred embodiment, the method
uses a system, such as device 10 of FIG. 2 including a charging
subsystem 44, to assist in determining values for the battery
voltage 120 and battery capacity. The charging current can be used
to determine the charging state and select either one of the curves
130,140. The charging subsystem 44 is typically capable of
performing several operations such as constant current charging
operation, constant voltage charging operation, and no charging--or
discharging--operation.
Referring now to FIG. 3, a flowchart illustrating the preferred
embodiment of the method of battery capacity reporting, is
described in reference to its steps.
At step 210, the battery voltage 120 is determined. At step 220, a
model 100 is provided, such as for example the model of FIG. 1. At
step 230, the last reported capacity is provided. At step 240, a
determination is made as to the charging state of the battery. For
instance if the battery charging current is determined, the
charging state can be derived from the sign of the charging
current. Although not expressly shown in the drawings, these first
four steps can in any order, or can performed simultaneously.
If at step 240, it is determined that the battery is charging, step
250C is taken. Conversely, if at step 240, it is determined that
the battery is discharging, step 250D is taken. Step 250C selects
the charge curve 140 whereas step 250D selects the discharge curve
130. At step 260, the charge curve model is applied to determine a
capacity based on the determined battery voltage of step 210 and
other factors.
Two embodiments of a method to carry out step 260 are currently
contemplated. FIGS. 5 7 illustrate a first embodiment. FIGS. 8 10
illustrate a second preferred embodiment which is easier to
understand in view of the first. Both embodiments will be described
in reference to FIG. 4.
FIG. 4 is an enlarged version of the dotted rectangular region 150
in FIG. 1. Shown is how the model 100 relates percent capacity 110
to battery voltage 120 for two charge states, the discharge state
curve 130 with points 132 and the charge state curve 142.
In the charge state, the capacity model 100 uses an inherent
property of battery charge current, the sign or charge state, to
relate battery voltage to capacity as a function of charge state at
step 260.
FIG. 5 illustrates a transition from the use of the charge curve
140 to the use of the discharge curve 130 of FIG. 4 in a first
embodiment of a method to carry out step 260 of FIG. 3.
A battery 48 is assumed to be initially charging 140 and at voltage
120 of 3.875 V, corresponding to point 142. Consequently, a 50%
capacity 110 is confidently determined. Next, the battery
transitions to the discharging state, for instance if power source
46 of FIG. 2 is disconnected.
A battery that has been charging for a while and has a voltage
reading of 3.875V, can be confidently gauged to be 50% full by
directly mapping off the initial charge curve, corresponding to a
charging state. If charging is turned off at this point, then the
battery's voltage would have to drop immediately to 3.825V in order
for it to map to 50% on the new charge curve, corresponding to a
discharging state. However, what is observed is that the battery
voltage actually takes some time (for instance tens of minutes, if
not more than an hour) to settle to 3.825V from 3.875V after
charging has stopped. During that time, mapping the voltage
directly off the new charge curve 330D would yield a capacity value
greater than 50%. If that value were reported directly, then the
user would see a reported battery capacity jump up to around 60%
when the device 10 is disconnected from the charger 46.
Line D--D defines a discharge region 300D. Two possible transitions
between the charge and discharge curves are shown as transition
320D and transition 330D relative to initial charge point 142.
Transitions 330D and 320D are illustrative only--several valid
transitions such as 320D and invalid transitions such as 330D can
be defined. They all have in common the fact that valid transitions
320D only allow the reported capacity to decrease when discharging,
whereas invalid transitions 330D cause the reported capacity to
increase while discharging.
FIG. 6 illustrates a transition from the use of the discharge curve
130 to the use of the charge curve 140 of FIG. 4 in a first
embodiment of a method to carry out step 260.
A battery 48 is assumed to be initially discharging 130 and at
voltage 120 of 3.825 V, corresponding to point 132. Consequently, a
50% capacity 110 is confidently determined. Next, the battery
transitions to the charging state, for instance if power source 46
of FIG. 2 is connected.
A battery that has been discharging for a period of time and has a
voltage reading of 3.825V can be confidently gauged to be 50% full
by directly mapping off the initial charge curve, corresponding to
a discharging state. If charging is turned on at this point, then
the battery's voltage would have to rise immediately to 3.875V in
order for it to map to 50% on the new charge curve, corresponding
to a charging state. However, what is observed is that the battery
voltage will actually take some time (for instance tens of minutes,
if not more than an hour) to settle to 3.875V from 3.825V after
charging has started. During that time, mapping the voltage
directly off the new charge curve 330C would yield a capacity value
lower than 50%. If that value were reported directly, then the user
would see a reported battery capacity jump down to around 30% when
the device 10 is connected to the charger 46.
Line C--C defines a charge region 300C. Two possible transitions
between the charge and discharge curves are shown as transition
320C and transition 330C relative to initial discharge point 132.
Transitions 330C and 320C are illustrative only--several valid
transitions 320C and invalid transitions 330C can be defined. They
all have in common the fact that valid transitions 320C only allow
the reported capacity to increase when charging, whereas invalid
transitions 330D would cause the reported capacity to decrease
while charging.
FIG. 7 is a flowchart illustrating a first embodiment of a method
to carry out step 260 of FIG. 3, in accordance to FIGS. 5 and
6.
System 10 provides the last reported capacity at step 410 and a
candidate capacity at step 420. At step 430, a determination is
made as to the charging state of battery 48, similar to step 240
already described in reference to FIG. 3. If the battery 48 is in
the charging state, then steps 440C, 450C or 460 are taken.
Conversely, if the battery is in the discharging state, then steps
440D, 450D or 460 are taken.
If the battery 48 is in the charging state, at step 440C, the
candidate capacity provided in step 420 is compared to the last
reported capacity provided in step 410. If the candidate capacity
is greater than the last reported capacity, then at step 450C the
candidate charge capacity provided at step 420 is used. Conversely,
if the candidate capacity is less than or equal to the last
reported capacity, the last reported capacity is used at step 460.
This ensures that only charge transitions 320C of FIG. 6 occur,
avoiding transitions of the type of 330C outside the charge region
300C.
If the battery 48 is in the discharging state, at step 440D, the
candidate capacity provided in step 420 is compared to the last
reported capacity provided in step 410. If the candidate capacity
is less than the last reported capacity, then at step 450D the
candidate discharge capacity provided at step 420 is used.
Conversely, if the candidate capacity is greater than or equal to
the last reported capacity, the last reported capacity is used at
step 460. This ensures that only discharge transitions 320D of FIG.
5 occur, avoiding transitions of the type of 330D outside the
discharge region 300D.
According to the method of FIG. 7, the reported capacity is only
allowed to increase when the battery is in a charging state.
Similarly, the reported capacity is only allowed to decrease when
the battery is in a discharging state.
When a change in charge state occurs, from the first initial charge
state to the second new charge state, it may take some time for the
battery to reach a new dynamic equilibrium at the second charge
state. During this transition period, it is possible that neither
the charge curve corresponding to the initial charge state nor the
charge curve corresponding to the new charge state provides a
sufficiently accurate voltage-to-capacity mapping. For instance, in
reference to FIGS. 5 6, a transition midway along line DD or CC
would have a constant 50% last reported capacity but could have a
voltage of 3.850 V, a point that is neither on the charge curve nor
on the discharge curve. This concept leads to the preferred
embodiment of a method to carry out step 260 of FIG. 3, which will
be discussed presently in reference to FIGS. 8 10.
FIG. 8 illustrates a transition from the last reported capacity 500
towards the discharge curve 130 of FIG. 4 in a preferred embodiment
of a method to carry out step 260 of FIG. 3. As compared to FIG. 5,
discharge area 300D is still defined by line DD. A "fast"
transition 520D replaces transition 320D. However, instead of
avoiding the reporting of all transitions 330D that might increase
reported capacity, a smaller charge "play" area 510D is defined by
line CC and "slow" transitions 530D through the charge play area
510D are allowed. "Fast" and "slow" are relative to one another so
that their cumulative long-term effect is to favour the reporting
of capacity decreases when in the discharge state. For example, a
"fast" transition might take 8.5 minutes to travel 80 percent of
the distance to the discharge curve 130 whereas a "slow" transition
might take 34.3 minutes. Note that transitions 330D outside the
play area 510D still do not cause a change in the reported
capacity.
FIG. 9 illustrates a transition from the last reported capacity
towards the charge curve of FIG. 4 in a preferred embodiment of a
method to carry out step 260 of FIG. 3. As compared to FIG. 6,
charge area 300C is still defined by line CC. A "fast" transition
520C replaces transition 320C. However, instead of "banning" all
transitions 330C that might decrease reported capacity, a smaller
discharge "play" area 510C is defined by line DD and "slow"
transitions 530C through the discharge "play" area 510C are
allowed. "Fast" and "slow" are relative to one another so that
their cumulative long-term effect is to favour the reporting of
capacity increases when the battery is in the charge state. For
example, a "fast" transition might take 1 minute to travel 80
percent of the distance to the discharge curve 130 whereas a "slow"
transition might take 17.2 minutes. Note that transitions 330C
outside the play area 510C still do not cause a change in the
reported capacity.
FIG. 10 is a flowchart illustrating a preferred embodiment of a
method to carry out step 260 of FIG. 3, in accordance to FIGS. 8
and 9.
At step 610, "fast" and "slow" transition rates are provided by
system 10. These rates can differ depending on whether the battery
is in a charge state or in a discharge state, as was described in
reference to FIGS. 8 and 9.
At step 620, a target capacity is provided by the system 10.
Preferably, the target capacity lies either on the charge curve 140
or the discharge curve 130 depending on whether the battery is in a
charge state or a discharge state, respectively.
At step 640, a "play" region is provided by the system 10.
Preferably, the "play" region varies with the slope of the charge
140 or discharge 130 curves, and is a function of the charge state.
For instance, if the last reported capacity while charging is less
than 7%, a 1% wide play region can be used, whereas if the last
reported capacity is greater or equal to 7%, a 6% wide play region
can be used. Similarly, if the last reported capacity while
discharging is greater than 10%, a 6% wide play region can be used,
whereas if the last reported capacity is smaller than or equal to
10%, a 1% wide play region can be used.
At step 640, a determination is made as to the charging state of
battery 48, similar to step 240 already described in reference to
FIG. 3. If the battery 48 is in the charging state, then step 650C
is taken, as well as 660C or 670,680 or 690. Conversely, if the
battery is in the discharging state, then step 650D is taken, as
well as 660D or 670,680 or 690.
If the battery is in a charging state, at step 650C, the target
capacity provided in step 620 is compared to the last reported
capacity. If the target capacity is greater than the last reported
capacity, then at step 660C a "fast" transition towards the charge
target capacity ensues. However, if the target capacity is less
than or equal to the last reported capacity, then at step 670, the
target capacity is checked with respect to the "play" region. If
the target capacity is within the play region, then at step 680 a
"slow" transition towards the charge target capacity ensues.
However, if the target capacity is outside the "play" region, then
at step 690 the last reported capacity is used.
If the battery is in a discharging state, at step 650D, the target
capacity provided in step 620 is compared to the last reported
capacity. If the target capacity is less than the last reported
capacity, then at step 660D a "fast" transition towards the
discharge target capacity ensues. However, if the target capacity
is greater or equal to the last reported capacity, then at step
670, the target capacity is checked with respect to the "play"
region. If the target capacity is within the play region, then at
step 680 a "slow" transition towards the discharge target capacity
ensues. However, if the target capacity is outside the "play"
region, then at step 690 the last reported capacity is used.
Although not expressly shown in the drawings, in another
embodiment, a corrected battery voltage is computed before
utilising the new charge curve. In order to compute the voltage
correction, a measured battery current is taken from the battery.
The value of the measured battery current can be positive or
negative, depending on the direction of current flow into or out of
the battery.
Using an effective serial resistance (ESR) for the battery, a
battery voltage correction term is obtained by multiplying the
value of the ESR for the battery and an estimated battery current.
The corrected battery voltage is obtained by adding the battery
voltage correction term to the estimated battery voltage while
taking into account the direction of current flow in the addition.
The estimated battery current can be determined by several ways,
such as by measurement. The corrected battery voltage is utilised
with the new charge curve in order to find a corresponding
capacity.
As used in this description and in the appended claims, ESR
corrected capacity reporting is defined as reporting a new capacity
by correcting the battery voltage based on ESR and an estimated
battery current prior to determining the capacity based on the
corrected battery voltage.
Furthermore, in yet another embodiment, in order to keep the
reported capacity from transitioning too abruptly, the reported
capacity is affected with the value of the corresponding capacity
progressively such that the reported capacity reaches the value of
the corresponding capacity at a convergence rate which is selected
from a multiplicity of convergence rates comprising a "fast"
convergence rate and a "slow" convergence rate. The determination
of which convergence rate to use is made as a function of the
difference between the last reported capacity and the charge curve
capacity, as well as the charge state of the battery. As used in
this description and in the appended claims, progressive capacity
reporting is defined as reporting a new capacity by a progression
from an initial capacity to the new capacity over time.
Although not explicitly shown in the drawings, temperature
corrections can be utilised throughout to ensure that the
temperature of the battery is also taken into account.
The above method is typically implemented as an embodiment of
charging subsystem 44. The system includes means for determining
the voltage of the battery and its present charge state. These
means provide the determined values to means for determining the
target capacity. The target capacity is determined according to the
methods described above and is then provided to a comparator, which
compares the target capacity with previous capacity. The result of
the comparison is used by target capacity adjusting means to adjust
the target capacity value. The adjustment can use any combination
of the methods described above to adjust the value of the battery
capacity.
As illustrated in FIG. 1 the charging subsystem 44 has voltage
reading means 700, charge state determining means 702, target
capacity determining means 704, a comparator 706, whose
functionality may be provided by microprocessor 38, and target
capacity adjusting means 708. The voltage reading means 700 are
operatively connected to the battery 48 to determine the voltage of
the battery 48. The charge state determining means 702 are
operatively connected to the battery 48 to determine the charging
state of the battery 48. The target capacity determining means 704,
are operatively connected to the voltage reading means 700 to
receive the determined voltage and to the charge state determining
means 702 to receive the determined charging state, so that they
can compute a target battery capacity based on the determined
voltage and the determined charging state. The comparator 706 is
operatively connected to the memory 710, which may be flash memory
24, RAM 26 or another memory system, to receive the previous
battery capacity value and to the target capacity determining means
704 to receive the target battery capacity. Comparator 706
generates a comparison signal representative of the comparison of
the previous battery capacity value and the target battery
capacity. The target capacity adjusting means 708 are operatively
connected to the comparator 706 to receive the comparison signal,
to the target capacity determining means 704 to receive the
determined target battery capacity and to the charge state
determining means 702 to receive the determined charging state. The
target capacity adjusting means 708 adjust the determined target
battery capacity if the comparison signal is not indicative of the
determined charging state, and they also store the adjusted target
battery capacity in the memory 710. Optionally, there may also be
reporting means 712, operatively connected to the target capacity
adjusting means 708 for reporting the adjusted target battery
capacity.
In various embodiments, the target capacity adjusting means 708
further includes means for a number of functions. One such function
is to adjust the determined target capacity to a capacity
determined from a predefined fast transition curve that models the
relationship between the determined battery voltage, the determined
present charging state and battery capacity after a change in
charging state. Another such function is to adjust the target
capacity to a capacity determined from a predefined slow transition
curve that models the relationship between the determined battery
voltage, the determined present charging state and battery capacity
when the target capacity is in a play region around the capacity of
the battery when the last change in charging state occurred.
In another embodiment the target capacity adjusting means 708 is
also connected to an effective serial resistance tester 714 which
is operatively connected to the battery 48 to determine an
effective serial resistance correction factor, the target capacity
adjusting means 708 further includes means for adjusting the target
capacity based on the effective serial resistance correction
factor. In embodiment of the present invention, the above described
system is integrated into a handheld computing or communicating
device.
The above-described aspects of the invention provide a system and
method that mitigate the uncertainty in battery capacity reporting
resulting from the transition between the charge and discharge
curves of the battery model that are present in the prior art.
Additionally the present invention accounts for the plastic
relationship between battery voltage and battery capacity.
The above-described embodiments of the present invention are
intended to be examples only. Alterations, modifications and
variations may be effected to the particular embodiments by those
of skill in the art without departing from the scope of the
invention, which is defined solely by the claims appended
hereto.
* * * * *
References